After a real close inspection of all 3 guns (1 96 and 2 92's) it would appear that the main point of contact is between the front part of the slide were the recoil spring seats and the dust cover rather than the rear lower part of the barrel and the frame. It looks like when the rear of the barrel contacts the frame it may be traveling at a higher speed than the slide when it contacts the dust cover, due to the barrel having been unlocked from the slide earlier in the recoil process. And I could be wrong here also! I'm pretty sure the 96 barrel weighs less than than the 92 barrel and as such carries less inertia when contacting the frame which may lessen this problem. This still doesn't explain the differences in the flatness of the machining in this area.

Interesting. I do believe you are right that the 96 barrel is lighter than the 92 barrel, bigger hole for the .40 means more material removed. This is why you often see .22 revolvers heavier than say a .357 revolver. Although I am not sure it carries less inertia as the .40 is a higher pressure round than the 9mm. I still believe your initial theory is correct that too much material was left on the outer edges of that part of the frame/rail which was causing it to be displaced backwards.

Dragline , It lasted a very short time !!
IIRC I made it from either 4140 or 4340 and heat treated it properly [I'm a metallurgist ] .After that I was cleaning some pistols and curious, I dropped a BHP spring into the pistol .It worked fine and was a stiffer spring .I had explained the whole thing to the fellow I sold it to and he said he never had a problem ! That's when I got the idea the original springs were made for 9mm Glisenti pressures.
Anyway the Walther has a similar locking wedge and I can't remember them having any problem ???
The only Beretta I have now is a nice O/U shotgun , it works fine !

My brand new M9 has marks similar to those. It just looks like where the steel was formed. I actually got my pistol the day before this thread was posted, so of course I checked it out when I saw this thread. I had only fired 10 rounds from it the first day, but the marks were there. I have about 200 through it now, and it hasn't gotten any worse. I don't think mine are a problem.

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